Currently, small base station devices provided in homes or offices have been studied. A small base station device is connected to, for example, a fixed line in a home and used to expand a communication area or provide user-specific service.
A small base station device is called home node B by the standardization group, 3GPP (3rd generation partnership project).
Further, a cell of a home node B that restricts users allowed to use the home node B by registering users allowed to access the home node B in advance is specifically called a CSG (closed subscriber group) cell (see Non-Patent Document 1). The CSG cell can also be called a femto cell, but their usage and meaning are the same.
A CSG cell in EUTRA (evolved universal terrestrial radio access) that is an evolved version of a third-generation mobile communication system has been studied by 3GPP.
A mobile station device incapable of identifying CSG cells in which its own terminal has been registered, CSG cells in which the terminal has not been registered, and normal cells attempts to access the CSG cells in which the terminal has not been registered, thus wasting consumption power or radio resource.
Accordingly, a technique capable of autonomously identifying that a mobile station device is located in an area of a registered CSG cell has been studied in EUTRA. Various methods may be used for a mobile station device to detect a registered CSG cell. For example, there is a method by which a mobile station device detects a registered CSG cell based on a position specified by a GPS (global positioning system) or IDs of a plurality of neighboring cells (Non-Patent Document 2).
When a mobile station device determines that its own terminal is located in an area of a registered CSG cell using one of the methods, the mobile station device initiates measurement of the CSG cell. When the measurement of the CSG cell in which the terminal has been registered can be performed for a reason such as discontinuous reception in the mobile station device, particular control for the measurement is unnecessary.
However, when a time to measure the CSG cell in which the terminal has been registered is not sufficient for a reason such as the mobile station device being in communication with the base station device (in an active state), requesting the base station device to create a gap for CSG cell measurement has been proposed (Non-Patent Document 3). A gap refers to an interval in which communication between a mobile station device and a base station device is not performed.
FIG. 28 is a sequence diagram illustrating a process in which a mobile station device requests a base station device to create a gap for CSG cell measurement. FIG. 29 is a sequence diagram illustrating another process in which the mobile station device requests the base station device to create the gap for CSG cell measurement. When the mobile station device is in communication with a base station device in a source cell and detects that the terminal is in an area of the CSG cell using one of the methods (step S001), the mobile station device transmits a gap request to the base station device in the source cell (step S002).
For the gap request, a message for the gap request may be transmitted or the gap request may be transmitted simultaneously with a measurement report message for reporting downlink reception quality from the mobile station device to the base station device in the source cell.
The base station device in the source cell having received the gap request transmits a gap control message including gap creation permission and gap information required for the gap to the mobile station device (step S003).
The gap information includes information required for the CSG cell measurement, such as a gap length (gap interval), start timing, and a period.
The mobile station device performs a CSG cell measurement process during the designated gap interval (a measurement process in the gap) (step S004). The mobile station device transmits content measured during the gap interval, as a measurement report message, to the base station device (step S005).
The base station device in the source cell instructs the mobile station device to stop the gap (step S006). The base station device instructs to stop the gap when the base station device determines that the CSG cell measurement is unnecessary based on the measurement report message in step S005 or when a predetermined time has elapsed from gap permission (step S106 in FIG. 29).
Since a process of steps S101 to S105 in FIG. 29 is the same as that of steps S001 to S004 and S006 in FIG. 28, the description thereof is omitted.
For a gap stop instruction, a handover instruction message (also referred to as a handover command) may be used instead. Alternatively, an available time of the gap may be designated upon the gap permission and an explicit message may be omitted.
In a CSG cell measurement process in a related art, a mobile station device autonomously detects that a terminal is located in an area of a CSG cell. Accordingly, when the CSG cell area is erroneously detected, when an installation site of the CSG cell is changed, or when the CSG cell is powered off, the CSG cell is not detected by the mobile station device and consumption power for the measurement is wasted.
When the base station device needs to create the gap interval for the CSG cell measurement, the mobile station device does not sufficiently use information on the CSG cell in which its own terminal has been registered even when the mobile station device has the information. Accordingly, an effective gap cannot be created.
Non-Patent Document 1: 3GPP TS36.300, Overall description; Stage2.V8.3.0 (http://www.3gpp.org/ftp/Specs/html-info/36300.htm)
Non-Patent Document 2: Huawei, “Cell re-selection for hNB”, R2-074831, 3GPP TSG-RAN WG2 Meeting #60, Jeju, South Korea, 5-9 Nov. 2007
Non-Patent Document 3: T-Mobile, et al. “Text proposal for CSG related mobility”, R2-075453, 3GPP TSG-RAN WG2 Meeting #60, Jeju, South Korea, 5-9 Nov. 2007